Help me to find a solution using UNIX commands

Shell Programming and Scripting
1

I have the below requirement. below is the content of the input file and my expected result
Input file: a.txt

<?xml version="1.0" encoding="UTF-8"?>
<Employee>
 <Name>XXXX</Name>
 <ID>1233</ID>
</Employee>
<?xml version="1.0" encoding="UTF-8"?>
<Employee>
 <Name>YYYY</Name>
 <ID>1345</ID>
</Employee>
<?xml version="1.0" encoding="UTF-8"?>
<Employee>
 <Name>AAAA</Name>
 <ID>1145</ID>
</Employee>

Output File:b.txt

<?xml version="1.0" encoding="UTF-8"?><Employee><Name>XXXX</Name><ID>1233</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?><Employee><Name>YYYY</Name><ID>1345</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?><Employee><Name>AAAA</Name><ID>1145</ID></Employee>

I am aware that we can acheive the output by using the below perl command

perl -plne 'BEGIN {$/=""} s/>\s*</></g' a.txt > b.txt

Could some one suggest a way to acheive the same using UNIX commands?

Thanks in Advance

2 
awk '{$1=$1}1' ORS="</ID></Employee>\n" RS="</ID>\n</Employee>" file
<?xml version="1.0" encoding="UTF-8"?> <Employee> <Name>XXXX</Name> <ID>1233</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?> <Employee> <Name>YYYY</Name> <ID>1345</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?> <Employee> <Name>AAAA</Name> <ID>1145</ID></Employee>
</ID></Employee>
3

Perl is as much of a Unix command today as AWK is. Like Paste.

$ paste -d"\0" - - - - - < file
<?xml version="1.0" encoding="UTF-8"?><Employee> <Name>XXXX</Name> <ID>1233</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?><Employee> <Name>YYYY</Name> <ID>1345</ID></Employee>
<?xml version="1.0" encoding="UTF-8"?><Employee> <Name>AAAA</Name> <ID>1145</ID></Employee>